Dye is utilized in fields such as a colorant for a polymer material and dichroic dye for liquid crystal, in addition to fields such as an electrophotographic light-sensitive material of an electrophotographic printer, a recording material for an optical disk, a non-linear optical material and a material for a near-infrared cut filter. Dye utilized in these fields, specifically infrared dye, shows low stability against light or heat, and is desired to be further improved.
On the other hand, in the fields of medical diagnosis and graphic arts, antihalation (AH) dye and antiirradiation (AI) dye have been commonly utilized to maintain sharpness despite reflection and refraction of incident light at the time of exposure. Specifically, characteristics required for AH dye and AI dye, utilized in a thermally developable photographic material, include absorption of a desired wavelength of light, no adverse influence to silver halide emulsion, and no residual contamination on the material after development. However, few infrared dyes, which provide maximum absorption in the near-infrared region, and specifically in the region of 700–900 nm, and with very low absorption in the visible region, are known, and an example disclosed includes squalirium dye (for example, refer to Patent Literature 1 and 2). When dye described in these sourses is utilized in a thermally developable photographic material, stability during high heat storage of the photosensitive material is unacceptable, and further improvement has been demanded.
[Patent Literature 1] JP-A 58-220143 (hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection)
[Patent Literature 2] U.S. Pat. No. 6,482,950